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The occurrence of Mine Acid Water is a natural phenomenon which is caused by the reaction of water and oxygen with sulphide bearing rock. The occurrence of natural rock sulphides with Oxygen and water can further enhance the production of sulphuric acid in mine water reservoirs due to the solubility of the sulphates present I n the rock along with SO2. It is a natural occurrence but also an environmental hazard.
The Mine Acid Water (MAW) is considered an environmental hazard particularly when combined with high soluble iron and sulphate content. The resultant water is limited in use as the low Ph combined with the iron staining can cause deterioration to decorative surfaces, elution of brass fittings, reduction in plant photosynthesis causing browning of lawns and vegetation, but more importantly it causes fish kills and mortality to all marine life when accidently discharged into creeks, rivers and waterways. The MAW also reduces the ability for plants to take up the water due to the low Ph and osmotic restrictions of the plant roots, thus killing or restricting the growth if used in the untreated state.
The remedy to mine acid water is to cause simultaneous oxidation of the iron sulphides and soluble metals to a precipitable residue. Alternative processes use lime or organic clays such as bentonite or polyacrylamide flocculants. This has been the approach in several countries but is not a cost-effective solution, further to the MAW problem is the disposal of the huge amount of sludge generated from these processes. The mine acid water at most open cut and other operating Queensland mines could be approached by a more scientific method, the application of a solution that causes rapid transformation of the iron and suspended metals, and then separation of the suspension by gravity precipitation in a settling pond.
The system comprises four main parts, Pumping, Dosing, Settling and Discharge, within these parts various control and sensing components complete the system.
A large capacity pump is used to draw MAW from the pit and distribute it to the Settling ponds
Within the above pump suction pipe, an automated dosing unit supplies our low cost chemical to both protect the pump and the neutralize the MAW
Ponds are made to accept the neutralized MAW from the pump via a ring main around the perimeter of the settling pond. This produces a non turbulent delivery into the ponds to start and assist in separation of the clear water and precipitate. Once treated, the Settling Pond clear water can be pumped to various services discussed elsewhere in this paper without any further treatment.
Pumps are fitted to keep the interface of settled sludge and water at an acceptable level and allow the transfer the treated clear water to where it is required.
The separation period can vary from minutes up to several hours depending on the dose rate of the solution, although tests conducted have indicated a period of less that 2 hours is sufficient for the separation to cause a stratification layer and provides the ability to remove the clear product water from the settling pond.
The design of the settling pond is subject to the volume of water required for on-site activities and usage per day, be that thousands or millions of litres. The water once treated with neutralising solution requires a settling period of up to 2 hours. If for example: if a requirement of 1 million litres per day (125,000 litres per hour) is desirable of useable treated water, the MAW would require a settling pond with a minimum capacity of 1,000,000 litres and for the incoming water to be placed in a manner that does not create turbulence in the settling pond. The treated water will have a settling effect in the pond and the clear treated water can be decanted or pumped out by using a surface floatation suction line connected to a pump capable of 125,000 litre per hour of discharge volume. This clear product water is suitable for use in the wash plant, dust mitigation on roads, washing vehicles without leaving streaks and general-purpose water on site. Also, the treated water with minor adjustment can be used for drinking water for livestock or broader application for growing of crops.
The daily water treatment is only limited to the capacity of the pumps and holding capacity of the settling pond.
The precipitated suspension will settle to the bottom of the pond. The settled sludge may have other avenues of valuable usage, the sludge may contain recoverable amounts of rare earth minerals and other valuable assets. The dark red sludge can be sold as a paint pigment or it has been suggested for use as a shark repellent.
The formulation of the treatment solution is customised for the exact application for each mine, the combination of the solution compounds are formulated to the analysis of the pit water, this analysis will vary from mine to mine depending on the type of sulphide rocks that are being disturbed during removal of overburden and extraction processes. The acid nature of the pit water will dissolve micro metal deposits from the surrounding rocks and overburden. These micro metal deposits which can be dissolved could be some of the rare earth metals which in their native state may not be viable for extraction, however once precipitated in the sludge may be a recoverable resource. An analysis of the pit water and dried sludge will indicate the presence of these valuable minerals and the combination of various compounds to effectively treat the pit water.
The Treated clear water once applied to the areas containing vegetation, will enhance the growth of plants as the Ph has been neutralised to a desirable range of 6.5 to 7.0 and the dissolved solids have been oxidised and changed into an available form suitable for nurturing plant growth. The organic sulphates have an effect of enhancing plant growth, it is well known that magnesium sulphate is a common nutrient used in agriculture.
The treatment method described was the main consideration to the discharge of the treated water into the environment, to this end samples of the untreated water along with samples of treated water were sent to a NATA Laboratory in Townsville for analysis. The Douglass Laboratory tested for dissolved solids, minerals, volatile organics, PCB’s, pesticides, herbicides and environmental hazards. The results showed
a substantial reduction in the Dissolved solids and presented no environmental hazards.
The Mine Water was sent to a Queensland Government NATA laboratory in Townsville for analysis both before treatment and following our treatment. The test results are available to any interested party. The positive results of the tests were confirmed by placing several small fish into one of the jars of treated water where the fish have for the past twelve weeks comfortably adapted to his new environment without any detriment. (see photo below)
The infrastructure required for establishing a MAW treatment system is reasonably simple, a pumping volume of useable water per day must be established in the first instance to dictate the size and volume of the settling pond, and the discharge rate of useable water required from the settling pond. The main pump for the MAW reservoir will be fitted with a dosing pump and Ph meter. The Ph sensor & dosing system form part of a closed loop control system supplying the dosing chemical into the transfer pump suction, thus keeping the Ph in the correct range at the settling pond.
This method causes the solution to be thoroughly mixed as it passes through the pump’s impeller. The discharge side of the pump should be directed into the settling pond in a manner that does not cause turbulence in the settling pond water, the settling pond needs to be a static body of water to allow the natural gravity to settle the precipitate. To achieve this with the volumes of water intended, a ring main should be made to surround the settling pond so the discharge water from the pump is sprayed into the air and allowed to fall into the settling pond like raindrops. This manner of application prevents turbulence in the settling pond and allows the precipitate to quickly settle. Further to this the aerial application of the water assists in oxygenation the water to further assist in micro-oxidation of any suspended solids.
Once the precipitate has settled a distinct strata or interface between the clear water and the settled minerals and metals is formed. An Interface sensor fitted to the settling pond will ensure the precipitate cannot be pumped with the clear water and advise the operator or automated system of the interface level at any given time.
A system is fitted within the settling pond to remove precipitate via a suction pipe at the bottom of the pond, this precipitate can be returned to the original pit if required or utilized for other valuable mineral separation activities.
Another pump is fitted to the settling pond to discharge the clear water using a floating suspended suction pipe within the pond, this clear water is then directed to where it is required around the mining site or local creeks.
A final Ph sensor is fitted to this clear water discharge point to prevent the unlikely discharge of out-of-range Ph water, the senser would in this case alarm and stop the discharge pump until adjustments are made.
The entire system could be automated after a trial period; however, the re-supply of chemical would be by regular delivery to the site.
Maintenance would be required at determined intervals to check pumps, piping, valves and sensors.
As the water is drawn and treated from the pit, an equal volume of soil and rock can be used and pushed into the pit. This progressive filling over time will keep a constant head of water and pressure on the pit bottom to prevent gases escaping exacerbating the problem. Further to this, the progressive filling of the pit will stabilise the flow of ground water and reinstate the hydrostatic water pressure on the surrounding aquifers. This will over time reinstate the natural groundwater flow through the disturbed aquifers. One million litres of removed water equals 1000 cubic meters of refill rock to maintain a balance.
This presents an ideal balance for reclaiming the pit with the surrounding overburden and eventually recovering the pit to be used for vegetive remediation. The refilling of the pit also excludes the overburden from water penetration which is one of the primary production points of the Mine Acid Water in the first place.
This Enviro Safe treatment process is simple to apply and cost effective, once the settling pond volume is established, the construction and implementation is quick and easy to have in production. Our company has joined hands with an approved mine construction contractor who can implement the design and construction of this system, The solution is a commercially confident product utilising a new application for a known product with a patent application underway to protect the formulation. This being said, Enviro Safe Water Treatment Pty Ltd is available to implement this technology at the desired mine site on a supply and management basis.
Several mine sites are trying to comply with the EPA regulations of reducing the volume of stored mine water to prevent accidental overflows in rain events. To achieve the reduction in volumes they are using “evaporators’ which consist of a very large diesel powered electric pump which are used to atomise the MAW and spray it into the air, besides being extremely costly to operate (up to $90,000 per megalitre) this method is discharging this acid mine water into the atmosphere. The mist drifts to where the wind dictates and as the mist is untreated the potential of expanding the contamination area is greatly enhanced. This evaporation method only moves the problem from the mine site to another place and possibly causes the effects of acid rain. I don’t think I would like to own a farm in the downwind of this mist.
MAW is an issue with most open cut and underground mine around the world, there are over 34,000 open cut pits in the USA, Australia has over 3,600 and Canada has a real serious problem with MAW, this Australian developed and patented solution can resolve most of the issues caused by MAW in gold, copper, and most other mineral
If you have a moment, please look on You-Tube at “Butte Montana copper mine”
The Deadly Seepage of Butte, Montana’s Berkeley Mine Pit – YouTube
you will see this is a world wide problem that we have found a low cost solution to Butte Montana Berkely mine where 10,000 geese died in one night after landing on the MAW reservoir.
This is a closed mine which now engages shooters to keep birds off the water. The shooters will have a job for life along with the next generations for ever until this water is treated. This is a perfect application for our product.